1. Field of the Invention
The present invention relates to an aqueous recording liquid suitable for inkjet recording, particularly, to a composition of a recording liquid featuring excellent characteristics in the case of using so-called plain paper, and also to a recording method and a composition suitable for the recording liquid. The present invention may be applied as aqueous ink compositions for aqueous writing instruments, recording instruments, and pen plotters.
2. Description of the Related Art
Various researches with inkjet printers have in recent years, been envisaged in order to improve printing properties and fastness of printing on plain paper being used. Particularly, color images on plain paper have been improved with a view for decreasing the blurring of printed letters and inter-colors bleeding.
Furthermore, researches have extensively been conducted in order to improve problems of waterproofing and of light fading or degrading. Particularly, while inkjet printers and plotters using ink employing pigments as coloring materials have been now available, they however still have more problems in reliability than those using dye ink, by occurrence of clogging or the like. In addition, while ink containing particles being colored by dyes or pigments has been investigated in order to prevent color bleeding, there still remains problem of clogging, caused by attaching of the ink to a nozzle portion.
An attempt for yielding higher quality of images has been carried out by use of dot density modulation art using inks more dense and lesser dense, in combination with area modulation art, in order to substitute silver emulsion photography by inkjet printing. As a result, high quality images being compatible to those given by silver emulsion photography are now reproducible on brightened paper. However, the resistibility for light fading is still insufficient, and the image quality on plain paper with regard to both density and chroma is poorer than those by electrophotography.
In order to improve the light resistibility, it has been attempted to add an ultraviolet absorbent or an antioxidant to inks. For example, Japanese Unexamined Patent Publication (Tokkai) No. 4-227773 discloses to add an ultraviolet absorbent having hydrophilic groups. However, the ultraviolet absorbent in aqueous ink is so readily crystallized that clogging is likely to occur.
Other attempts for adding dye-chelated compound into ink have been carried out to prevent fading. For example, suppression of fading has been designed by adding xcex2-cyclodextrin into a light purple-magenta ink, but, it leads to a significant increase of viscosity. Therefore if an ink being concentrated enough is used, adding of the xcex2-cyclodextrin into the ink of high density sufficient to make it possible chelating will be suffered from a difficulty to eject ink, due to an increased viscosity.
It also has been attempted to improve the reliability by forming chelated compounds of cyclodextrin with coloring material, in order to prepare insoluble and highly water-resistant colors. Japanese Patent No. 2612661 discloses an ink obtained by forming a chalated compound of cyclodextrin or polycyclodextrin including an alcohol-soluble or oil-soluble dye, and dissolving the chelated compound in the ink. However, for some types of dye, sufficient reliability in reproducing dense enough images cannot be attained.
Moreover, Japanese Unexamined Patent Publication (Tokkai) No. 11-506800 discloses an attempt to ensure the reliability and to improve light resistibility by bonding an ultraviolet absorbent with cyclodextrin. However, for some types of dye, sufficient effects also cannot be attained.
On the other hand, for the purpose of suppressing the bleeding in the boundary of colors, efforts to find out compounds to be used in ink have been made, according to which a compound is added to precipitate at least one coloring material in the ink. For example, Japanese Unexamined Patent Publication (Tokkai) No. 10-219160 discloses an ink set using color ink containing a water-soluble calcium salt or magnesium salt, together with a comparatively highly water-soluble dye as coloring material, thereby suppressing the bleeding on boundary of printings is made. The cited Publication also says that the bleeding may often be countered by use of black ink having a slow permeability. Japanese Unexamined Patent Publication (Tokkai) No. 11-323225 discloses an ink set using ink containing a quaternary ammonium salt and/or a water-soluble polyvalent metal salt, to suppress the bleeding on the boundary of printings. Which may be happened in case of self-dispersion of carbon ink having a slow permeability is used. However, the water resistibility of such color inks is not sufficient, because of there are only limited varieties in combination of dyes capable of adding salts therein are investigated.
For the purpose of improving the suitability of ink for plain paper various attempts to modify the ink using pigment, colored particles or the like as a coloring material from a view of improving reliability, have been researched to improve the reliability of ink using pigment. For example, Japanese Unexamined Patent Publication (Tokkai) No. 10-330665 discloses pigments ink using self-dispersible carbon particles and using urea or urea derivatives. The cited also discloses inks having resinous particles being colored by dyes or pigments, and showing improved reliability by adding urea or the like.
While those types of inks are preferable in recording with recording head having a high ejection pressure and utilizing thermal energy, its ejection characteristics in the case of actuator driven by piezoelectricity or electrostatic force may however be affected by ammonia or carbon dioxide generated by decomposing of the urea. In the case of using thermal energy too, the reliability may often be deteriorated in the head being contacted with ink, depending on head material.
In addition to the influence of carbon dioxide from atmosphere, acidic substance being eluted into ink, which makes lowered the pH of ink, may occur especially during high temperature storage, to make deteriorating of components being contacted with the ink. This phenomenon is particularly noticeable in the case of inks having some types of dyes or self-dispersing carbon particles.
It is the first object of the present invention to provide a recording liquid and an ink for inkjet recording which satisfy various characteristics and show an excellent coloring property on plain paper, with high durability of image in storage such as light fastness and the like, and improved reliability.
It is the second object of the present invention to provide more preferable scheme of compound salts to be added the recording liquid for the purpose of improving the above-mentioned properties.
It is the third object of the present invention to provide more preferable and defined mode of above-mentioned compound salts.
It is the fourth and the fifth objects of the present invention to provide more preferable and defined mode achievable excellent safety of the compound salts.
It is the sixth object of the present invention to provide a recording liquid and an ink for inkjet recording which make them capable of suppressing the bleeding on the boundary of colors, and capable of improving light stability and the water resistibility.
It is the seventh object of the present invention to provide an additive preferably used without affecting color tone of images.
It is the eighth object of the present invention to provide a recording liquid and an ink for inkjet recording which show preferable color reproducibility on plain paper, with improved light stability.
It is the ninth object of the present invention to provide a recording liquid and an ink for inkjet recording which show an improved light stability, a balanced color tone with a water resistibility on plain paper.
It is the tenth object of the present invention to provide a recording liquid and a pigment ink for inkjet recording which has a high water resistibility and light resistibility, and a high reliability with more improved anti-bleeding property on the boundary of colors, compared to those by prior arts.
It is the eleventh object of the present invention to provide a recording liquid and a pigment ink for inkjet recording which have an excellent reliability in printing system.
It is the twelfth object of the present invention to provide a recording liquid and a pigment ink for inkjet recording which have a excellent fixability and a high reliability.
It is the thirteenth object of the present invention to provide a recording liquid and a pigment ink for inkjet recording which have a high ejection stability even after a long time pause.
It is the fourteenth object of the present invention to provide a recording liquid and a pigment ink for inkjet recording which have a high ejection stability, especially excellent water resistibility and bleeding resistibility on the boundary of colors.
It is the fifteenth object of the present invention to provide a recording liquid and an ink for inkjet recording, which are endowed an improved color reproducibility and an improved chromatic property on plain paper, and are obtainable images having high light stability.
It is the sixteenth object of the present invention to provide a recording liquid and an ink for inkjet recording using colored particles, thereby an excellent reliability in printing system and the minimized degree of image degradation are shown.
It is the seventeenth object of the present invention to disclose a water-soluble or mixable organic solvent to be added into the ink, in order to provide a moisture-retaining property to ink and to provide a suitable range of properties to hold ejection stability.
It is the eighteenth and the nineteenth objects of the present invention to disclose an embodiment having improved wettability to a recording medium.
It is the twentieth object of the present invention to disclose a range for favorable combinations of the ink or recording liquid and other materials used in printing system, from a view of system""s durability and stability, with excellent compatibility of the recording liquid or the ink.
It is the twenty-first object of the present invention to disclose a recording method that can form good images with using of the ink.
It is the twenty-second object of the present invention to provide an ink cartridge that can form good images with using of the ink.
It is the twenty-third object of the present invention to provide an inkjet equipment that can form good images with using of the ink.
Above-mentioned objects are achieved in accordance to the present invention featuring characteristics as described hereinafter; which comprises;
(1): A recording liquid comprising a coloring material, an organic solvent to disperse or to dissolve the coloring material, and water, wherein the recording liquid further comprises a compound represented by the following formula (1) in the form of free acid or a salt thereof. 
xe2x80x83Where x is 4 to 8;
(2): The recording liquid according to above described (1), wherein the salt is one of selected from the group consisting of an alkali metal salt, a quaternary ammonium salt, an alkanolamine salt, and a quaternary phosphonium salt;
(3): The recording liquid according to above described (1) or (2), wherein the alkali metal salt is of lithium salt;
(4): The recording liquid according to any one of above described (1) to (3), wherein the quaternary ammonium salt has at least one hydroxyl group;
(5): The recording liquid according to any one of above-described (1) to (4), wherein the alkanolamine is one of selected from the group consisting of ethanol amine, diethanol amine, and triethanol amine;
(6): The recording liquid according to any one of above described (1) to (5), comprising a polyvalent metal ion source compound releasable polyvalent metal ion consisting, in the alkaline state, of a compound represented by above mentioned formula (1) and a phenolate complex;
(7): The recording liquid according to above described (6), wherein the polyvalent metal ion source compound is, at least one, of selected from the group consisting of an alkaline-earth metal salt, a lanthanoid metal salt, an aluminum salt and a zinc salt, and of vested with a solubility more than or equal to 1 g/100 g in water;
(8): The recording liquid according to any one of above described (1) to (7), wherein the coloring material is a dye;
(9): The recording liquid according to above described (8), wherein the dye has at least one sulfonic acid group and/or carboxylic acid group therein;
(10): The recording liquid according to any one of above described (1) to (7), wherein the coloring material is a pigment;
(11): The recording liquid according to above described (10), wherein the pigment is particles with average size 10 to 300 nm;
(12): The recording liquid according to above described (10) or (11), wherein the coloring material is a pigment and being dispersed in water by a dispersant, and said dispersant is bonded to one or more of carboxyl group.
(13): The recording liquid according to above described (10) or (11), wherein the coloring material is a pigment, and said pigment being improved in its surface by bonding of a hydrophilic group or groups, and said pigment being dispersed in water;
(14): The recording liquid according to above described (13), wherein one or more of hydrophilic group is bonded to the surface of the pigment is one or more of carboxyl group;
(15): The recording liquid according to any one of above described (1) to (7), wherein the coloring material is a particles being colored by a dye or a pigment;
(16): The recording liquid according to above described (15), wherein the colored particles have an average size 10 to 300 nm;
(17): The recording liquid according to any one of above described (1) to (16), comprising a water-soluble or water-mixable organic solvent of the recording liquid containing at least one water-soluble or water-mixable organic solvent selected from the group consisting of glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, tetraethylene glycol, 1,6-hexanediol, 2-methyl-2-, 4-pentanediol, polyethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, thiodiglycol, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone;
(18): The recording liquid according to any one of above described (1) to (17), wherein the recording liquid containing at least one surfactant selected from salt of poly-oxyethylene alkyl ether acetate, salt of dialkyl sulfosuccinate, poly-oxyethylene alkyl ether, poly-oxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene block copolymer and acetylenic glycol-based surfactants;
(19) The recording liquid according to any one of above described (1) to (18), wherein the recording liquid containing polyhydric alcohol alkyl ether and/or diol having or more of carbon atoms.
Above-mentioned objects are also achieved in accordance of the present invention featuring characteristics as described hereinafter; which also comprises;
(20) The recording liquid according to any one of above described (1) to (19), wherein the pH of the recording liquid is adjusted to 6 to 11.
Above-described objects can also be achieved in accordance to the present invention featuring characteristics as follow;
(21) A recording method by ejecting the recording liquid according to any one of above described (1) to (20), characterized by ejecting the ink as small droplets by action of thermal energy or mechanical energy, and attaching the droplets to a material to be printed having sized degree of 3 seconds or more by Stoeckigt Sizing Degree determination conducted by the test method of JIS P-8122, and by reproducing printings with the resolution degree not less than 10 dots/mmxc3x9710 dots/mm fineness, and with the amount of ink attached on the material to be recorded is 1.5 g/m2 to 30 g/m2.
Above described objects can also be achieved in accordance to the present invention featuring characteristics as follow;
(22): A recording liquid cartridge comprising a recording liquid reservoir containing a recording liquid, wherein the contained recording liquid is of the recording liquid according to any one of above described (1) to (20).
Above described objects can also be achieved in accordance to the present invention featuring characteristics as follow;
(23): An inkjet recording apparatus comprising a recording liquid reservoir or a recording liquid cartridge containing a recording liquid, or a recording liquid cartridge, and a head portion or a recording unit for ejecting the recording liquid in form of droplets by action of thermal energy or mechanical energy, wherein the recording liquid according to any one of above described (1) to (20) is used as the recording liquid.
Calix[n]arene-p-sulfonic acid represented by following formula (1) used in the present invention has phenollic hydroxyl groups and acts as an antioxidant. This calix compound itself is disclosed in Japanese Unexamined Patent Publication (Tokkai) No. 4-100890. Furthermore, the calix[n]arene-p-sulfonic acid can coordinate other compounds having hydrophobic group or groups inside of ring, the same as that other chalating sources can react with ligands to form chelating. It is also known that this kind of OH group forms a complex bonding with metal ions (J. of The Chemical Society of Japan, 583, N09, 1999). Moreover, this calix compound is characterized by a high solubility in water because it has sulfonic acid groups so that it is dissolved by 8 to 20% in water at 25xc2x0 C., although it depends on the number of x.
In particular, it has become clear that the degree of dissociation of the sulfonic acid group and the phenollic OH group to transform to free form are changed, depending on the value of pH, thereby ability of making complex of the organic cation with metal ion is also changed, thus, the resulted complex can always work as an antioxidant having a function to prevent the fading or discoloring of pigment, and furthermore, a function to suppress the bleeding on the boundary of colors can be provided, too.
Hereinafter is given by an example of the compound represented by formula (1) of the present invention, and by modified examples in cases of high pH and low pH of them. 
Where a metal ion or an organic cation is shown as a phenolate complex, M represents a coordinator, and N+ represents a monovalent cation.
It has become evident that in the high pH state, it is possible to suppress the aggregation of coloring material positioned in the ink, and in the low pH state, the coloring material makes it to be more insoluble, or to be more reduced one in solubility for water, providing the water resistively.
Furthermore, it has become evident that the compound of formula (1) captures polyvalent metal ions caused by contamination during ink production or recording system operation, or includes the hydrophobic groups of the coloring material, in the case of high pH, thereby the storage properties can be improved.
It was found that while the coloring material having conventional formulation shows a significant pH reduction by high temperature storage or by the influence of carbon dioxide or the like, the compound of formula (1) of the present invention however improves storage durability and receptivity of the ink using the same conventional coloring material, by improving its pH buffering property, with making the inclusion of organic cations such as alkali metal ions, quaternary ammonium and phosphnium and the like, to form chelated compound.
It was also found that above mentioned function as an antioxidant results the effect of suppressing the deterioration of the members to be contacted with the ink in printing system, to prevent corrosion of them.
The ink of the present invention can be used satisfactorily in printers utilizing pressure by PZT force, printers with vibration plate bent ejecting ink by electrostatic force, drop-on-demand inkjet printers of bubble jet system utilizing boiled film, and any other printers with so-called charge control systems for charging ink electrically while vibrating the ink by PZT plate. In particular, the ink of the present invention is so highly reliable that it can be ejected with a stability by through a mall nozzle having a diameter of 20 xcexcm or less.
Regarding the source of calix[n]arene-p-sulfonic acid represented by formula (1), namely, calix[4]arene, calix[5]arene, calix[6]arene, calix[7]arene, and calix[8]arene, they are able to be sulfonated with concentrated sulphuric acid at about 80xc2x0 C. to yield corresponding sulfonic acid salts used in the present invention. They are, however as for as sodium salts are concernd, available from Acros Organics Corp., as CALX-S4, CALX-S6, and CALX-S8 from Sugai Chemical Industry Corp. Ltd.
Impurities can be removed from these compounds by subjecting the crude compounds to recrystallization with using mixture of water and methanol. Removal of inorganic salts such as sodium chloride can be conducted by treating aqueous solutions thereof, with a reverse osmosis membrane, ion-exchange resin, an ultrafiltration membrane or the like. In particular, in order to enhance the reliability, the compound of formula (1) is contained in the form of a lithium salt as an alkali salt, or in the form of a quaternary ammonium salt, a phosphonium salt or an alkanolamine salt in the recording liquid so that the stability of it can be improved.
Examples of the hydroxides of quaternary ammonium and phosphonium which can produce preferable salts when used in combination with the compound of formula (1) may include compounds of following formula (I), and specific examples thereof are, for example, those shown in Table 1. 
Where X represents nitrogen or phosphorus, R1 to R4 represent hydrogen, alkyl groups having 1 to 4 carbon atoms, hydroxyalkyl groups, or halogenated alkyl groups.
It is preferable to change the calix [n]arene compound into its salts of the hydroxides, especially, of (I-2), (I-4) and (I-7) having a hydroxyl group in Table 1. They provide the most excellent storage durability. It is preferable that the hydroxide is neutralized in an amount of at least 0.3 times moles thereof with the sulfonic acid group of the calix [n]arene compound. Alternatively, a part of the phenol hydroxyl group may be neutralized.
In the present invention, examples of the water-soluble salts to be added for the purpose of suppressing the bleeding in the boundary of inter colors, or of improving light fastness and waterproofing property of the dye are, for instance, quaternary ammonium salts or polyvalent metal salts. In particular, the salts of polyvalent metal ions used preferably are those capable of chelating with the compound represented by formula (1) to form a phenolate complex therewith. Examples of the ions are as for Be2+, Mg2+, Ca2+, Sr2+ and Ba2+ of the alkaline-earth metals, Al3+. Ga3+, In3+ and Sn4+ of the Group ITTE of the Periodic Table, Ti4+, Fe3+, Co2+and Cu2+ of the transition metals and La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+ and Gd3+ of the lanthanoid metals.
In particular, highly water soluble alkaline earth metal salts, lanthanoid metal salts, zinc salts, they have a solubility in water of 1 g/100 g or more, are preferable because they easily form a phenolate complex or salt with the compound represented by formula (1) when being dissolved in water.
Specific examples thereof are as for magnesium nitrate (42.1 g), magnesium sulfate (26.7 g), magnesium chloride (35.5 g), lanthanum chloride (49.27 g), lanthanum nitrate (56.1 g), lanthanum sulfate (2.25 g), calcium chloride (45.3 g), calcium nitrate (57.98 g), and zinc nitrate (56.1 g).
The amount of these salts to be added can be suitably selected depending on the characteristics of the coloring material used in the ink set for forming color images, but it is added preferably in an amount of 0.1 to 10 wt. %. An amount of 0.1 wt. % or less provides little effect, and an amount of 10 wt. % or more is more likely to cause sedimentation due to temperature change, or poor ejection due to evaporation of water existing near by nozzle.
The amount of the coloring material in the ink of the present invention is ranging from 0.1 to 20 wt. %, and preferably 0.2 to 8 wt. %, depending on purposes of application. An amount of 0.1 wt. % or less does not provide coloring ability, even if it is used for light color ink, and an amount of 20 wt. % or more provides excessively high viscosity so that ejection is difficulty.
The water-soluble dye used in the present invention can be used in combination with other coloring materials, if necessary. As the water-soluble dye used in the present invention, dyes classified into acid dyes, direct dyes, basic dyes, reactive dyes, food dyes stated in The Color Index, that have excellent waterproofing property and light resistibility, can be used.
Specific examples of these dyes are as follows. Examples of acid dyes and food dyes are as for C.I. Acid Yellow 17, 23, 42, 44, 79 and 142, C.I. Acid Red 1, 8, 13, 14, 18, 26, 27, 35, 37, 42, 52, 82, 87, 89, 92, 97, 106, 111, 114, 115, 134, 186, 249, 254 and 289, C.I. Acid Blue 9, 29, 45, 92 and 249, C.I. Acid Black 1, 2, 7, 24, 26 and 94, C.I. Food Yellow 3 and 4, C.I. Food Red 7, 9 and 14 and C.I. Food Black 1 and 2. Examples of direct dyes are as for C.I. Direct Yellow 1, 12, 24, 26, 33, 44, 50, 86, 120, 132, 142 and 144, C.I. Direct Red 1, 4, 9, 13, 17, 20, 28, 31, 39, 80, 81, 83, 89, 225 and 227, C.I. Direct Orange 26, 29, 62 and 102, C.I. Direct Blue 1, 2, 6, 15, 22, 25, 71, 76, 79, 86, 87, 90, 98, 163, 165, 199 and 202 and C.I. Direct Black 19, 22, 32, 38, 51, 56, 71, 74, 75, 77, 154, 168 and 171. Examples of basic dyes are as for C.I. Basic Yellow 1, 2, 11, 13, 14, 15, 19, 21, 23, 24, 25, 28, 29, 32, 36, 40, 41, 45, 49, 51, 53, 63, 64, 65, 67, 70, 73, 77, 87 and 91, C.I. Basic Red 2, 12, 13, 14, 15, 18, 22, 23, 24, 27, 29, 35, 36, 38, 39, 46, 49, 51, 52, 54, 59, 68, 69, 70, 73, 78, 82, 102, 104, 109 and 112, C.I. Basic Blue 1, 3, 5, 7, 9, 21, 22, 26, 35, 41, 45, 47, 54, 62, 65, 66, 67, 69, 75, 77, 78, 89, 92, 93, 105, 117, 120, 122, 124, 129, 137, 141, 147 and 155 and C.I. Basic Black 2 and 8. Examples of reactive dyes are as for C.I. Reactive Black 3, 4, 7, 11, 12 and 17, C.I. Reactive Yellow 1, 5, 11, 13, 14, 20, 21, 22, 25, 40, 47, 51, 55, 65 and 67, C.I. Reactive Red 1, 14, 17, 25, 26, 32, 37, 44, 46, 55, 60, 66, 74, 79, 96, 97 and 180 and C.I. Reactive Blue 1, 2, 7, 14, 15, 23, 32, 35, 38, 41, 63, 80 and 95. Especially, acid dyes and direct dyes can be used preferably.
Furthermore, dyes of the Projet (product name) series such as Projet Cyan 2, Projet Magenta 2, and Projet Yellow 2 produced by Avecia that were developed as dyes for inkjets are also preferable.
The dyes to which sulfonic acid or carboxylic acid being introduced are particularly preferable in the present invention, because of their balance of waterproofing property with reliability. While specific examples are the dyes shown in Table 2, which are described in form of free acid, the present invention is however not limited thereto.
Examples of pigments used in the present invention are as follows. Examples of organic pigments are as for azoes, phthalocyanines, anthraquinones, dioxazines, indigos, thioindigoes, perylenes, isoindolinones, aniline black, azomethines, rhodamine B lake pigment, and carbon black. Examples of inorganic pigments are as for ferric and ferrous oxides, titanium dioxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, indigo blue, cadmium red, chrome yellow, and metal powder.
More specifically, examples of pigments for black are as for carbon black (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black and channel black; metallic materials such as copper oxide, iron oxide (C.I. Pigment Black 11) and titanium dioxide; and organic pigments such as aniline black (C.I. Pigment Black 1).
Examples of pigments for color ink are as follows. Examples of pigments for yellow ink are as for C.I. Pigment Yellow 1 (Fast Yellow G), 3, 12 (Disazo Yellow AAA), 13, 14, 17, 23, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 150, and 153. Examples of pigments for magenta are as for C.I. Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant Fast Scarlet), 23, 31, 38, 48:2 (Permanent Red 2B (Ba)), 48:2 (Permanent Red 2B (Ca)), 48:3 (Permanent Red 2B (Sr)), 48:4 (Permanent Red 2B (Mn)), 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81 (Rhodamine 6G lake), 83, 88, 92, 101 (red iron oxide), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (dimethylquinacridone), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, and 219. Examples of pigments for cyan are as for C.I. Pigment Blue 1, 2, 15 (copper phthalocyanine blue R), 15:1, 15:2, 15:3 (phthalocyanine blue R), 15:4, 15:6 (phthalocyanine blue E), 16, 17:1, 56, 60, and 63.
For medium colors, the following pigments can be used alone or in combination for red, green and blue: C.I. Pigment Red 177, 194 and 224, C.I. Pigment Orange 43, C.I. Pigment Violet 3, 19, 23 and 37, C.I. Pigment Green 7 and 36 or the like.
For black, carbon black produced by a furnace method or a channel method and having an average particle size by the primary particles of 15 nm to 40 nm, a specific surface area of 50 to 300 m2/g according to a BET adsorption method, a DBP oil absorption of 40 to 150 ml/100 g, volatile content of 0.5 to 10% and pH of 2 to 9 is used as carbon black, and in particular, acid carbon black having pH 6 or less is preferable because of its high density. Carbon black treated with hypochlorous acid, carbon black treated with sulfonating agent, carbon black having a free anionic group such as sulfonic acid and carboxylic acid introduced by treating with a diazonium compound is more preferable. As yellow pigment, C.I., Pigment Yellow 74, 128, and 138, which contain no Benzidinyl skeleton, are preferable. As magenta pigment, quinacridone-based C.I., Pigment Red 122, and 209 are preferable. As cyan, C.I., Pigment Blue 15:3, aluminum-coordinated phthalocyanine, and metal-free phthalocyanine as phthalocyanine compounds, are preferable.
For these organic color pigments, where they have a sulfonic acid group or carboxylic acid being introduced, by for example a surface treatment, thereby the dispersion stability of the pigment therein is improved, and thereby they have a dispersion stability without dispersing agent, they should be used preferably as self-dispersing pigments. Furthermore, the use of pigments whose surfaces are capsulated, and the use of pigments in which polymer being grafted and the like, can change ink to an ink having excellent dispersion stability and high reliability.
First, 300 g of commercially available acid carbon black of pH2.5 (manufactured by Cabot Corporation, under commodity name of MONARCH 1300) were mixed sufficiently in 1000 ml of water, and 450 g of sodium hypochlorite (available chlorine concentration of 12%) were dripped into the mixture, followed by stirring at 100 to 105xc2x0 C. for eight hours. Then, 100 g of sodium hypochlorite (available chlorine concentration of 12%) were further added to this solution and the solution was dispersed by a lateral type of dispersing machine for three hours. The resultant slurry was diluted with water by a factor of 10, and the pH was adjusted with lithium hydroxide, followed by desalination and concentration with an ultrafiltration membrane until an electric conductivity of 0.2 mS/cc was reached. Thus, a carbon black dispersing liquid having a pigment concentration of 15% was obtained. Large particles were removed by centrifugation, and further the carbon black dispersing liquid was filtrated with a 1 micron nylon filter. The resultant carbon black dispersing liquid was denoted as carbon black dispersing liquid  less than 1 greater than . The total content of Fe, Ca and Si was 100 ppm or less according to ICP measurement. The concentration of chlorine ions was 10 ppm or less. The average particle size (D50%) measured by the Microtrack UPA was 95 nm.
First, 150 g of commercially available carbon black pigment (manufactured by Degussa Corporation, under product name of Printex#85) were mixed sufficiently in 400 ml of sulfolane, and the mixture was dispersed minutely by a ball mill. Then, 15 g of amidosulfuric acid were added to the mixture, followed by stirring at 140 to 150xc2x0 C. for 10 hours. The resultant slurry was fed into 1000 ml of ion exchanged water and subjected to centrifugation at 12000 rpm so that a surface-treated carbon black wet cake was obtained. This carbon black wet cake was dispersed again in 2000 ml of ion exchanged water, and the pH was adjusted with lithium hydroxide, followed by desalination and concentration with an ultrafiltration membrane. Thus, a carbon black dispersing liquid having a pigment concentration of 10% was obtained. This liquid was filtrated with a 1 micron nylon filter, and the resultant liquid was denoted as carbon black dispersing liquid  less than 2 greater than . The total content of Fe, Ca and Si was 100 ppm or less according to ICP measurement. The concentration of sulfuric acid ions was also 100 ppm or less. The average particle size was 80 nm.
First, 100 g of carbon black having a specific surface area of 230 m2/g and a DBP oil absorption of 70 ml/100 g and 34 g of p-amino-N-benzoic acid were mixed and dispersed in 750 g of water, and 16 g of nitric acid were dripped to the mixture and stirred at 70xc2x0 C. After five minutes holding, a solution of 11 g of sodium nitrite dissolved in 50 g of water was added thereto, followed by further stirring for one hour. The resultant slurry was diluted by a factor of 10, and subjected to centrifugation to remove large particles. The pH was adjusted to 8 to 9 with diethanolamine, followed by desalination and concentration with an ultrafiltration membrane. Thus, a carbon black dispersing liquid having a pigment concentration of 15% was obtained. This liquid was filtrated with a 0.5 xcexcm polypropylene filter, and thus the resultant liquid was denoted as carbon black dispersing liquid  less than 3 greater than . The total content of Fe, Ca and Si was 100 ppm or less according to ICP measurement. The concentration of nitric acid ions was 10 ppm or less. The average particle size was 99 nm.
A solution at about 75xc2x0 C. containing 2 liters of water and 43 g of sulfanilic acid was added to 202 g of carbon black having a surface area of 230 m2/g and a DBPA of 70 ml/100 g under stirring. This mixture was cooled to room temperature under stirring, and 26.2 g of concentrated nitric acid was added thereto. A solution of 20.5 g of sodium nitrite in water was added. A 4-sulfobenzenediazonium hydroxide inner salt was prepared and reacted with the carbon black. The dispersed system was stirred until bubbling was stopped. The resultant slurry was diluted, and the pH was adjusted to 8 to 9 with lithium hydroxide and large particles were removed by centrifugation, followed by desalination and concentration with an ultrafiltration membrane. Thus, a carbon black dispersing liquid having a pigment concentration of 15% was obtained. This liquid was filtrated with a 1 xcexcm polypropylene filter, and thus the resultant liquid was denoted as carbon black dispersing liquid  less than 4 greater than . The total content of Fe, Ca and Si was 100 ppm or less according to ICP measurement. The concentration of nitric acid ions was 50 ppm or less. The average particle size was 95 nm.
As a yellow pigment, a pigment was prepared by treating C.I. Pigment Yellow 128 with low temperature plasma, and introducing a carboxylic acid group. A dispersing liquid of this pigment in ion exchanged water was subjected to desalination and concentration with an ultrafiltration membrane to provide a yellow pigment dispersing liquid  less than 1 greater than  having a pigment concentration of 15%. The average particle size was 70 nm, and the total content of Fe, Ca and Si was 100 ppm or less.
In the same manner, a magenta dispersing liquid  less than 1 greater than  having a pigment concentration of 15% was prepared as a magenta pigment, using C.I. Pigment Magenta 122. The average particle size was 60 nm, and the total content of Fe, Ca and Si was 100 ppm or less.
In similar manner, a cyan dispersing liquid  less than 1 greater than  having a pigment concentration of 15% was prepared as a cyan pigment, using C.I. Pigment Cyan 15:3. The average particle size was 80 nm, and the total content of Fe, Ca and Si was 100 ppm or less.
In the present invention, a pigment dispersing liquid using a dispersant for pigment can be used. Examples of dispersants for pigment are as follows. As hydrophilic polymer, examples of natural polymer are as for vegetable polymers such as arabian gum, tragacanth gum, guar gum, karaya gum, locust bean gum, arabinogalactan, pectin and quince seed starch, seaweed polymers such as alginic acid, carrageenan and agar, animals polymers such as gelatin, casein, albumin and collagen, and microbial polymers such as xanthan gum and dextran. Examples of semisynthetic hydrophilic polymer are as for cellulose polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose, starch polymers such as sodium carboxymethyl starch and starch sodium phosphate ester and seaweed polymers such as sodium alginate and propylene glycol ester alginate. Examples of pure synthetic hydrophilic polymer are as for vinyl polymers such as poly vinylalcohol, poly vinylpyrrolidone and poly vinylmethyl ether, uncrosslinked polyacrylamide, polyacrylic acid and alkali metal salts thereof, acrylic resins such as water-soluble styrene acrylic resin, water-soluble styrene maleate resin, water-soluble vinylnaphthalene acrylic resin, water-soluble vinylnaphthalene maleate resin, polyvinylpyrrolidone, polyvinyl alcohol, alkali metal salt of xcex2-naphthalenesulfonic acid formalin condensation product, high molecular weight compounds having salts of cationic functional groups such as quaternary ammonium and amino groups in their side chain and natural high molecular weight compounds such as shellac.
In particular, those to which a carboxylic acid group being introduced such as those containing copolymer of homopolymer of acrylic acid, methacrylic acid, and styrene acrylic acid or monomer having other hydrophilic groups are preferable as a high molecular weight dispersant.
In the case of using a surfactant, anionic surfactants such as polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl ether acetate, and nonionic surfactants such as nonylphenyl ether can be used.
yellow pigment: C.I. Pigment Yellow 128,
magenta pigment: C.I. Pigment Red 122,
cyan pigment: C.I. Pigment Blue 15:3,
dispersant A: nonionic surfactant manufactured by Kao Corporation, Emulgen 913), HLB15.5,
dispersant B: acrylic resin aqueous solution manufactured by Johnson Polymer, Joncryl 611 (neutralized with ammonia, solid content of 20%), acid value of 57.
(1) Salt Milling Particle-Size Reduction Processing
First, 250 parts of the pigment, 2500 parts of sodium chloride and 200 parts of diethylene glycol were fed in a 1 gallon kneader made of stainless steel (manufactured by Inoue Seisakusho Co. Ltd.), and kneaded for three hours. Next, this mixture was fed into 2.5 liters of hot water, and was stirred by a high-speed mixer for about one hour while being heated to about 80xc2x0 C. to be formed slurry. Then, filtration and washing with water were repeated five times to remove sodium chloride and the solvent, so that dry pigment was obtained.
(2) Surface Treatment Processing
First, 20 parts of the pigment, 5 parts (in terms of solid content) of the dispersants A and B and water were added to a paint conditioner such that the total amount was 100 parts and the mixture was dispersed for three hours. The resultant aqueous pigment dispersion was subjected to centrifugation at 15000 rpm for six hours.
Then, 0.1 parts of 30% ammonia water and 79.9 parts of purified water were added to 20 parts of the surface-treated pigment of Reference Example 5, and dispersed again in a paint conditioner, so that a pigment concentrated solution was prepared. For the pigment that had not been subjected to surface treatment, 5 parts (in terms of solid content) of the dispersants A (formulation 1) or the dispersant B (formulation 2) and purified water were added to 20 parts of the pigment such that the total amount was 100 parts and this mixture was dispersed in a paint condition, followed by purification with a reverse osmosis membrane. Thus, a concentrated recording liquid for inkjet was prepared. The concentrated liquid was filtrated with a 1 xcexcm nylon filter and further filtrated with 0.5 xcexcm polypropylene filter to provide a dispersing liquid for use. The content of Fe, Ca, and Si in all the cases was 100 ppm or less.
The average particle sizes of the dispersing liquids were as follows:
yellow dispersing liquid  less than 2 greater than : 93 nm
yellow dispersing liquid  less than 3 greater than : 80 nm
magenta dispersing liquid  less than 2 greater than : 60 nm
magenta dispersing liquid  less than 3 greater than : 56 nm
cyan dispersing liquid  less than 2 greater than : 90 nm
cyan dispersing liquid  less than 3 greater than : 87 nm
In the present invention, particles being colored by dyes or pigments is used as a coloring material so that the fixability and the color development on plain paper are improved, and the use of water-soluble calixarene of formula (1) associated with the colored particles leads to the preparation of recording liquid having the nature hard to be aggregated. As the colored particles, either high molecular weight particles or inorganic particles such as silica and alumina can be used. It is preferable to use high molecular weight particles for the purpose of providing an improved brightness.
In particular, it is preferable to use a colored high molecular weight material particles, such as particles based an acrylic or polyester impregnated with a dye or a pigment, that is, the particles in which a dye or a pigment may be present on a surface layer or in internal portion, or over whole body. A specific example is colored particles produced by a method disclosed in Japanese Unexamined Patent Publication No. 2000-53898. One example thereof close to these obtained by the disclosed method is as follows.
First, 20 parts by weight of methyl ethyl ketone as a polymerization solvent and monomer having the following composition for initial feeding as a polymeric unsaturated monomer and a polymerization chain transfer agent were fed in a sealable reaction vessel provided with stirring blade, a tube for cooling medium and a tube for introducing nitrogen gas, and nitrogen gas purge was performed sufficiently.
The mixed solution in the reaction vessel was warmed to 65xc2x0 C. while being stirred in a nitrogen atmosphere. Besides this processing, the following monomer for dropping into the vessel, following chain transfer agent for polymerization 60 parts of methyl ethyl ketone, and 0.2 parts of 2,2xe2x80x2-azobis(2,4-dimethyl valeronitrile) were mixed, and sufficient purge with nitrogen was performed, then the resultant mixed solution was gradually dripped in the reaction vessel over three hours.
By two hour passing after finished dropping, a solution of 0.1 parts by weight of 2,2xe2x80x2-azobis(2,4xe2x80xa2dimethyl valeronitrile) dissolved in 5 parts by weigh of methyl ethyl ketone was added thereto, and further aged at 65xc2x0 C. for two hours and at 70xc2x0 C. for two hours so that a vinyl based polymer solution was obtained.
A part of the obtained vinyl based polymer solution was dried at 105xc2x0 C. for two hours under a vacuumed pressure to remove the solvent completely for isolation. Average molecular weight by the weight was about 10,000 and Tg was 180xc2x0 C.
Then, obtained vinyl based polymer is dried under a vacuumed pressure to obtained the dried one, then, to 5 g of the vinyl based polymer obtained by the drying, 25 g of toluene and 5 g of anthraquinone dye having the following composition were added, and complete dissolving was made, and 2 g of a sodium hydroxide solution were added thereto to neutralize a part of the acidic groups of the vinyl based polymer. Then, 300 g of ion exchanged water was added thereto and the mixture was stirred, followed by emulsificating for 30 minutes using the Nanomaker TM (manufactured by Nanomizer Co., Ltd.), which is an emulsifying apparatus. Obtained emulsified product was concentrated by removing toluene completely at 60xc2x0 C. under a vacuumed pressure, and removing a part of water. Then, impurities such as monomer were removed with an ultrafiltration membrane and thus a magenta dispersing liquid  less than 4 greater than  of vinyl based polymer particles impregnated with purified dispersive dye (average particle size of 98 nm, a solid concentration of 10%) was obtained. 
By use of similar manner with the exception of C.I. Disperse Yellow 118 as the dye, a yellow dispersing liquid  less than 4 greater than  (average particle size of 98 nm, a solid concentration of 10%) was obtained, and also by use of similar manner with the exception of C.I. Disperse Blue 36 was used as the dye, a blue dispersing liquid  less than 4 greater than  (average particle size of 98 nm, a solid concentration of 10%) was obtained.
In the present invention, the wettability to the recording paper can be improved by using a surfactant. Examples of preferable surfactants are as for interfacial polyoxyethylene alkyl ether acetate, dialkyl sulfosuccinate, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polyoxypropylene block copolymer and acetylenic glycol based surfactants. More specifically, by using polyoxyethylene alkyl ether acetate (II) and/or dialkyl sulfosuccinate (III) having a branched alkyl chain with 5 to 7 carbon chains, the characteristics on plain paper can be improved, and the stability of dissolved and dispersed coloring agent further can be obtained.
Rxe2x80x94Oxe2x80x94(CH2CH2O)mCH2COOMxe2x80x83xe2x80x83(II)
Where R represents an alkyl group having 6 to 14 carbon atoms that may be branched, and M represents an alkali metal ion, quaternary ammonium, quaternary phosphonium or alkanolamine, and m is 3 to 12. 
Where R5 and R6 represent branched alkyl groups having 5 to 7 carbon atoms, and M represents an alkali metal ion, quaternary ammonium, quaternary phosphonium or alkanolamine.
Furthermore, the surfactant exhibits excellent dissolution stability by using lithium ions, quaternary ammonium or quaternary phosphonium represented by the above mentioned general formula (I), as the counter ions of the surfactant in the present invention.
Examples of preferable nonionic surfactants are as for a surfactant of general formula (IV), which is polyoxyethylene alkyl phenyl ether, and a surfactant of general formula (V), which is an acetylenic glycol based surfactant. Utilizing them in combination of themselves, increases the permeability as a multiplier effect, and thus ink having reduced bleeding on the boundary of colors and a less blurring of printed letters can be obtained. 
Where R represents a carbon chain having 6 to 14 carbon atoms that may be branched, and k is 5 to 12. 
where p and q are 0 to 40.
When the pH of this ink is 6 or more, the storage stability of the ink can be obtained. The most parts of the electrography paper or letter papers used in offices have a pH of 5 or 6. In accordance with the present invention, the ink is ejected at a speed of 5 to 20 m/s in the form of droplets having an ejection weight of 2 ng to 50 ng from a fine outlet of 9 to 60 xcexcm diameter on these kinds of paper for recording on so-called plain paper having a Stoeckigt Sizing Degree of 3 seconds or more according to the test method of JIS P-8122 with an adhered amount of a single color of 1.5 g/m2 to 30 g/m2, and thus a recording method for forming high quality and high resolution images can be realized. However, when pH is 9 or more, the properties may be changed easily with degradation of the surfactant of formula (III) during storage, therefor it is preferable that the pH is 6 to less than 9 when the surfactant of formula (III) is used.
The surfactants of an amount between 0.05 wt. % and 10 wt. % of formulae (II), (III), (IV) and (V) for addition in the present invention leads to a desired permeability to the ink with characteristics required by a printer system. An amount of 0.05% or less causes bleeding on the boundary portion where two colors are superimposed in all the cases. The use of an amount of 10 wt. % or more at a low temperature causes precipitating of the compound itself, which is a mark of poor reliability.
Next, Table 3 shows a list of tangible surfactants (II) and (III) of the present invention in the form of free acid.
For the ink of the present invention which is basically intended the use of colored particles, even where water is used as a liquid solvent, but the following water soluble organic solvents can be used for the purpose of providing the ink with the desired properties, for preventing the ink drying during production and recording, and for improving the dissolution stability of the compounds used in the present invention or the like. Examples thereof are as for polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,2-hexanediol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol and petriol, polyhydric alcohol alkylethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether and propylene glycol monoethyl ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone and xcex5-caprolactam; amides such as formamide, N-methylformamide, formamide and N,N-dimethylformamide; amines such as monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine and triethylamine, sulfur-containing compounds such as dimethylsulfoxide, sulfolane and thiodiethanol, propylene carbonate, ethylene carbonate, xcex3-butyrolactone and the like. These solvents can be used alone or in combination with a plurality of them together with water.
Among these, particularly preferable examples are as for diethylene glycol, thiodiethanol, polyethylene glycol 200 to 600, triethylene glycol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, petriol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, N-methyl-2-pyrrolidone, N-hydroxyethylpyrrolidone, 2-pyrrolidone and 1,3-dimethylimidazolidinone. With using the above, excellent effects can be obtained with high solubility of the compound of the present invention and avoiding of poor jetting caused by evaporation of water content.
In particular, in the present invention, preferable examples of the solvent to provide the dispersion stability of the coloring agent are as for pyrrolidone derivatives such as N-hydroxyethyl-2-pyrrolidone.
Furthermore, examples of penetrating agents to be added for the purpose of adjusting the surface tension other than the surfactants (II) to (V) are as for alkyl and aryl ethers of polyhydric alcohols such as diethylene glycol monophenyl ether, ethylene glycol monophenyl ether, ethylene glycol monoallyl ether, diethylene glycol monophenyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, triethylene glycol monobutyl ether and tetraethylene glycol chlorophenyl ether, diols such as 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol and 2,2-dimethyl-1,3-propanediol, polyoxyethylene polyoxypropylene block copolymer, fluorochemical surfactant, and lower alcohols such as ethanol and 2-propanol. Particularly preferable example are as for diethylene glycol monobutyl ether as a polyhydric alcohol alkyl ether, and 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol as diols having 6 or more carbon atoms. Diols are suitable because they hardly cause water-insoluble coloring material to aggregate. The amount thereof to be added depends partly on the type and the desired properties, but they are added in a range of 0.1 to 20 wt. %, and preferably 0.5 to 10 wt. %. At an amount of less than the lower limit, the permeability is insufficient, and an amount of more than the upper limit adversely affects the characteristics for forming particles. Furthermore, the addition of them improves the wettability to the ink jet head members or recording instruments so that the filling properties are improved, and thus poor recording due to bubbles hardly occurs.
The properties of the ink of the present invention can be adjusted as appropriate for the system. Herein, the surface tension of ink is an indicator that indicates the permeability into paper, and measuring of dynamic surface tension of ink should be conducted with in short time of one or less second after the surface to be measure is prepared, thereby determined value well corresponds to the permeability of the ink measured. This is different from figures on a static surface tension determined by the period of time consumed in reaching saturation. The dynamic surface tension can be measured according to any of conventionally known methods such as one described in Japanese Unexamined Patent Publication (Tokkai) No. 63-31237 that enables to measure a dynamic surface tension with in short time as period of one second or less. The surface tension is preferably 50 mN/m or less, more preferably 40 mN/m or less, for excellent drying properties. On the other hand, in view of the stability of the ejecting of the ink drops, if the dynamic surface tension is too low, unstable forming of liquid particles is brought. The dynamic surface tension allowing stable ejection is preferably 40 mN/m or more at 1 ms.
The viscosity range can be selected with appropriateness between 1 mPaxc2x7s and 10 mPaxc2x7s, depending on the ejection method.
Regarding the range of the pigment particle size of the ink, particles with 10 nm to 300 nm are used, and an average particle size of 60 nm to 120 nm is preferable, The solid content of a range from 1 to 25 wt. % in the ink is preferable, and the water content in a range from 25 to 93 wt. % is preferable, more preferably 50 to 80 wt. %.
In the present invention, a range of the conductivity that does not impair the dispersion stability is desired, and in view of the "xgr" electric potential of particles colored by pigments or dyes and existing in the ink, preferable electric conductivity of the ink is 1 mS/cm to 6 mS/cm, thereby dispersibility of the particles in ink is satisfied, therefore the ink is rendered to highly reliable one showing only small change in particle size over long time of period, consequently high enough reliability is attained with its ink.
As a rule, attempts to add an agent or the like for adjusting conductivity have been envisaged, in order to make the conductivity close to above mentioned range, however, above mentioned compound of formula (1) in the present invention has free type of and different kinds of groups, and an adjusting of the content of the free groups makes it possible to hold the conductivity in above mentioned range. Furthermore, a fine adjustment concerned it, is can be attained by adding an agent for adjusting the conductivity which doesn""t inhibit dispersibility. Preferable examples of this type of conductivity adjusting agent are as for quaternary ammonium salts such as tetramethyl ammonium chlorides, and alkanolamine salts.
In addition to the coloring agent and the solvent as described above, conventionally known additives can be added to the ink of the present invention. For example, as an antiseptic or an antifungal agent, sodium dehydroacetate, sodium sorbate, 2-pyridinethiol-1-oxide sodium, sodium benzoate, pentachlorophenol sodium, isothiazoline and the like can be used in the present invention.
As a pH adjusting agent, any substance can be used, as long as it can adjust the pH to 7 or more without adversely affecting the ink.
Tangible examples are as for amines such as diethanolamine and triethanolamine, hydroxides of alkali metal elements such as lithium hydroxide, sodium hydroxide and potassium hydroxide, ammonium hydroxide, quaternary ammonium hydroxide, quaternary phosphonium hydroxide, carbonates of alkali metals such as lithium carbonate, sodium carbonate and potassium carbonate.
As chelating reagents, for example, sodium ethylenediamine tetraacetate, sodium nitrilotriacetate, sodium hydroxyethyl ethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uramil diacetate and the like can be used.
As rust-preventive agents, acid sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropyl ammonium nitrite, pentaerythritol tetranitrate, dicyclohexylammonium nitrite and the like can be used.
Other than the above, water-soluble ultraviolet absorber, or water-soluble infrared absorber can be added, depending on the purposes of application.